The present invention relates to a granular form of a mixture of a nickel-quencher and a benzophenone.
More specifically, the present invention relates to a granular form of a mixture of a nickel-quencher and a 2-hydroxy-4-alkyloxybenzophenone, a process for its preparation and its use as a light stabilizer for agricultural films based on polyolefins or olefinic copolymers.
The present invention also relates to agricultural films based on polyolefins or olefinic copolymers stabilized with the above granular form and greenhouses covered with these films.
Nickel-quenchers are at present sold in fine powder form and their use causes problems of environmental pollution, health and the safety of the operators in the feeding and handling phase.
A benzophenone is also generally used in the stabilization of agricultural films, together with nickel-quenchers.
Conventional methods for obtaining a physical form of nickel-quencher with a low powder content (for example, compaction of the powders under pressure) tested on both the nickel-quencher alone, and on mixtures of nickel-quenchers and benzophenones, have proved to be inapplicable or have not given satisfactory results.
The Applicant has now found a granular form of a mixture of a nickel-quencher and a benzophenone capable of overcoming the drawbacks of the known art.
The present invention therefore relates to a granular form of a mixture comprising:
(a) a nickel-quencher corresponding to [2,2xe2x80x2-thio-bis(4-t-octyl-phenolate)-n-butylamineNickel (II)] having formula (I): 
(b) a 2-hydroxy-4-alkyloxybenzophenone corresponding to 2-hydroxy-4-n-octyloxybenzophenone having formula (II): 
xe2x80x83characterized in that it has two diffraction lines at angles 2xcex8=17.593 and 2xcex8=22.023 in the X-Ray diffraction spectrum from powders.
The X-Ray diffraction spectrum from powders is carried out using Cu-Kxcex1 radiation (xcex=1.54178).
In the granular form of the present invention, the nickel-quencher (a) having formula (I) and the benzophenone (b) having formula (II) are used in a ratio ranging from 0.4 to 3, preferably in a ratio ranging from 1 to 2.
The nickel-quencher (a) having formula (I) is known under the following trade-names: Cyasorb UV 1084 of Cytec, or Chimassorb N-705 of Ciba.
The benzophenone (b) having formula (II) is known under the following trade-names: Lowilite 22 of Great Lakes, Chimassorb 81 of Ciba, or Cyasorb UV 531 of Cytec.
The granular form of the present invention can be obtained according to the following process.
A process for the preparation of the granular form of the present invention comprises:
(1) dissolving, under stirring, the nickel-quencher (a) having formula (I) in the benzophenone (b) having formula (II) which has been previously melted at 50xc2x0 C.;
(2) cooling the solution obtained as described under point (1).
Step (1) of the above process is carried out at a different temperature depending on the ratio between the nickel-quencher (a) having formula (I) and the benzophenone (b) having formula (II), used: step (1) of the present invention is generally carried out at a temperature ranging from 50xc2x0 C. to 150xc2x0 C., preferably between 50xc2x0 C. and 120xc2x0 C.
The cooling according to step (2) of the above process, suitable for causing the solidification of the solution obtained as described in point (1), can be obtained with any of the methods known in the art.
The preferred methods consist in:
pouring the solution onto a cold metal plate maintained, for example, at a temperature equal to or less than room temperature: in this case the solid obtained must be granulated so as to obtain granules having the desired dimensions;
dripping the solution onto a cold metal plate maintained, for example, at a temperature equal to or less than room temperature: in this case drops are obtained already having the desired dimensions.